Less is more: What it means to warm the planet one degree

In the midst of Chicago’s scorcher of a summer, one degree warmer didn’t mean very much. One hundred degrees compared to 101? The plain and simple answer: it was hot out.

But for climate scientists such as Aaron Putnam and Sean Birkel, one degree means a lot more.

They talk in the standard scientific unit of temperature - degrees centigrade - and use this measurement to calculate the earth’s overall temperature.

In degrees centigrade, the planet has gotten approximately 1 degree warmer since the 1950’s, according to climate scientists. That’s about 1.8 degrees Fahrenheit. In passing, this may sound as insignificant as small changes in this summer’s rising temperatures. But when put in perspective, it adds up to a lot.

“You can see huge dynamical changes in what appear to be pretty small changes in global temperature,” said Putnam, who is a postdoctoral research scientist at Columbia University’s Lamont-Doherty Earth Observatory in New York. During the last global ice age, the planet was only 6 degrees centigrade cooler than it is today, he said.

“One degree is one-sixth of the ice age,” Putnam said. “I think it just shows how little cooling you need to cause big changes across the planet,” he added.

It took 2,000 years for the earth’s temperature to warm 6 degrees centigrade, finally pulling it out of the last ice age, Putnam explained. With this in mind, 1 degree centigrade over the last century is one-sixth of a drastic change in global temperature.

And in the Arctic, where ice caps that play a large role in regulating temperature are found, warming has been even more significant.

“If we look at the Arctic in just the last 10 years, much of the Arctic has warmed probably on average 4 degrees centigrade, maybe even 5 degrees centigrade as a response to a loss of Arctic sea ice cover,” said Birkel, a postdoctoral research fellow at the University of Maine. That's a whopping 7-9 degrees Fahrenheit in the place that's warming fastest on the globe.

The Arctic is a key player in climate change, because melting there impacts all of the earth’s intertwined climate systems.

“Winters are changing quite dramatically because of this Arctic melt,” Birkel said. In mid-September, when the annual ice melt comes to an end, the ice loss in the Arctic hit a new record high, he said. “So 2012 is uncharted territory. There’s a new minimum in Arctic sea ice. The Arctic today is not what it was 10 years ago. It’s much different. There’s no doubt that winters are warming in response to this.”

With changes in Arctic sea ice, the planet’s global hydrology—the way water is naturally distributed throughout the planet—will be amplified. Dryer places will receive less rain and wetter climates will receive more, exacerbating each region’s natural affinity for drought or flooding.

And there are other practical implications of one degree of climate change as well, such as the spread of infectious disease.

“Ten to 15 years ago, it wasn’t a big deal,” Birkel said, referring to infections such as Lyme disease, which have migrated north as winters have become shorter and warmer. “Now it is - people in New England know about it.”

Frozen ground and subzero temperatures kill the insects that carry diseases such as Lyme and West Nile. If they can survive the winter, they have a greater ability to move farther north, carrying disease. The spread of malaria, a mosquito-borne disease that kills millions of people every year, is among the worst threats of climate change.

Birkel and Putnam said they cannot predict what the future holds, partly because climate is so complex.

“It’s really a web of nonlinear systems,” Birkel explained. “Climate scientists understand them for the most part, but slight changes can make a big difference.”